The present invention is useful for aligning two pulses, and more particularly for varying the delay of one pulse in relation to a reference signal until that pulse is conincident with the second pulse.
Travelling wave tube (TWT) amplifiers are in widespread use for high gain amplification of radio frequency (RF) signals. To obtain the amplified RF power from the TWT, it is necessary for the input RF signal to be provided to the TWT at the same time the cathode current is applied. TWT amplifiers are often operated in pulsed applications and when employed with a duty factor above 1%, liquid cooling of the TWT is typically required for reliable operation. In certain applications, liquid cooling is undesirable due to weight, bulk, or other reasons. Where high power levels are required and liquid cooling cannot be used it becomes essential to maximize the efficiency of air-cooled, pulsed TWT amplifier.
Optimum performance of a pulsed TWT amplifier requires coincidence of the RF input pulse with the TWT cathode current. A system trigger signal is normally employed as a reference. The TWT cathode current pulse is started after a fixed delay from the leading edge of the system trigger pulse. The RF exciter pulse or input RF signal to the TWT is also typically started at a predetermined time interval after the leading edge of the system trigger pulse. If the delay for starting the cathode current pulse is too small, the cathode current beam pulse energy and TWT duty cycle are wasted during the early part of the beam period before the RF input signal is applied, resulting in a reduction of the amplified RF pulse width. Conversely, too long a delay in starting the cathode current pulse results in wasted cathode current beam pulse energy and TWT duty cycle during the latter part of the beam period after the RF input pulse has ended, with a resultant reduction of the amplified RF pulse width. The desired situation for efficiency is a coincident RF input pulse with a cathode current pulse so that energy is wasted from neither pulse.
Insofar as is known to applicants, the timing adjustment to align the RF input pulse for coincidence with the TWT beam current pulse has heretofore been performed manually, with the operator employing an oscilloscope to display the two pulses and manually adjusting the cathode current pulse delay to obtain coincidence with the RF input pulse to the TWT. A moderate degree of operator skill and experience are required as well as the time to make this adjustment properly. Under certain field conditions, it is undersirable to require the use of test equipment, experienced maintenance personnel, and relatively long times to align the pulses.
It would be an advance in the art to provide a means for minimizing the necessity for field operator intervention during field alignment of TWT RF amplifier equipment.
It would further be advantageous to provide a means for aligning automatically two pulses without the need for operator intervention and the concommitant potential for erroneous adjustment.
It would further be advantageous to be able to align the pulses frequently and with relatively little equipment "down-time" in the case where the equipment operating environment varies drastically and such variances may affect alignments.